CNGNGE JOHN MCMURRY CHAPTER 27 Synthetic Polymers Organic Chemistry with Biological Applications
CHAPTER 27 Synthetic Polymers
Polymers Large molecules built up by repetitive bonding together of monomers Indicate repeating unit in parentheses H2C=CH CH2-CH-I Styrene Polystyrene
▪ Large molecules built up by repetitive bonding together of monomers ▪ Indicate repeating unit in parentheses Polymers
Why This Chapter? More comprehensive view of polymers to see: More detail about how polymers are made How polymer structure correlates with their physical properties
More comprehensive view of polymers to see: ▪ More detail about how polymers are made ▪ How polymer structure correlates with their physical properties Why This Chapter?
27-1 Chain-Growth Polymers Chain-growth polymers are produced by chain-reaction polymerization Benzoyl peroxide is used as common radical initiator Initiator (radical,acid,or anion)adds to a carbon- carbon double bond of an unsaturated substrate (a vinyl monomer)to yield a reactive intermediate that reacts with a second molecule of monomer and so on 2C02 Benzoyl peroxide Benzoyloxy Phenyl radical radical(Ph) Repeat Ph-CH2CH2. many times → Ph-(CH2CH2)nCH2CH2
Chain-growth polymers are produced by chain-reaction polymerization ▪ Benzoyl peroxide is used as common radical initiator ▪ Initiator (radical, acid, or anion) adds to a carbon– carbon double bond of an unsaturated substrate (a vinyl monomer) to yield a reactive intermediate that reacts with a second molecule of monomer and so on 27-1 Chain-Growth Polymers
27-1 Chain-Growth Polymers Acid-catalyzed (cationic)polymerization is effective only with vinyl monomers that contain an electron-donating group (EDG) n EDG stabilized the chain-carrying carbocation intermediate EDG EDG EDG EDG EDG EDG A H2C=CH H-CH2-CH+ H2C=CH CH3CH-CH2CH+ Repeat CH2-CH方 where EDG an electron-donating group Cengoge Learing.All Rights Poserved
Acid-catalyzed (cationic) polymerization is effective only with vinyl monomers that contain an electron-donating group (EDG) ▪ EDG stabilized the chain-carrying carbocation intermediate 27-1 Chain-Growth Polymers
27-1 Chain-Growth Polymers Isobutylene (2-methylpropene)is an example of a monomer that polymerizes rapidly under cationic conditions Carried out commercially at-80'C using BF3 and water to generate BF3OH-H+catalyst CH3 CH3 BF3OH-H+ H2C=CH 十CH2-CH Isobutylene Polyisobutylene
Isobutylene (2-methylpropene) is an example of a monomer that polymerizes rapidly under cationic conditions ▪ Carried out commercially at ‒ 80 ˚C using BF3 and water to generate BF3OHˉ H+ catalyst 27-1 Chain-Growth Polymers
Anionic Polymerization Vinyl monomers with electron-withdrawing substituents (EWG)can be polymerized by anionic catalysts Chain-carrying step is nucleophilic addition of an anion to the unsaturated monomer by a Michael reaction EWG EWG EWG EWGEWG EWG Nu:- Nu-CH2-CH:- H2C=CH NuCH2CH-CH2CH:- Repeat CH2-CH where EWG an electron-withdrawing group
▪ Vinyl monomers with electron-withdrawing substituents (EWG) can be polymerized by anionic catalysts ▪ Chain-carrying step is nucleophilic addition of an anion to the unsaturated monomer by a Michael reaction Anionic Polymerization
Examples of Anionic Polymerization Products Acrylonitrile (H2C=CHCN),methyl methacrylate [H2C=C(CH3)CO2CH3],and styrene (H2C=CHCH5)polymerize anionically -Styrofoam cups are prepared anionically using stryene with butyllithium as the catalyst T八 Bu:-Li+ H2CCH Bu-CH2-CH:- Repeat -CH2-CH-In Styrene Polystyrene
▪ Acrylonitrile (H2C=CHCN), methyl methacrylate [H2C=C(CH3 )CO2CH3 ], and styrene (H2C=CHC6H5 ) polymerize anionically ▪ Styrofoam cups are prepared anionically using stryene with butyllithium as the catalyst Examples of Anionic Polymerization Products
Examples of Anionic Polymerization Products n“Super glue”is a anionic polymer of methyl a- cyanoacrylate which contains two EWGs Nu: CN Nu-CH2-C: CH2 C-OCH3 C-OCH3 Methyl a-cyanoacrylate H2C=C Dermabond (2-ethylhexyl a-cyanoacrylate) -OCH2CHCH2CH2CH2CH3 O= CH2CH3
▪ “Super glue” is a anionic polymer of methyl acyanoacrylate which contains two EWGs Examples of Anionic Polymerization Products
27-2 Stereochemistry of Polymerization: Ziegler-Natta Catalysts Polymerization of a substituted vinyl monomer can lead to numerous chirality centers on the chain A polymer having all groups on the same side of the zigzag backbone is called isotactic If the groups alternate on opposite sides of the zigzag backbone,it is called syndiotactic Randomly oriented groups are called atactic polymers
▪ Polymerization of a substituted vinyl monomer can lead to numerous chirality centers on the chain ▪ A polymer having all groups on the same side of the zigzag backbone is called isotactic ▪ If the groups alternate on opposite sides of the zigzag backbone, it is called syndiotactic ▪ Randomly oriented groups are called atactic polymers 27-2 Stereochemistry of Polymerization: Ziegler–Natta Catalysts